1. Field of the Invention
The present invention relates to an apparatus for discriminating the kind of a sheet material.
2. Related Background Art
Recently, sheet-material discriminating apparatuses for discriminating the kind of a sheet material have received attention in various technological fields. For example, it is desirable to automatically detect the kind of paper for use in printers, copiers and other image forming machines for keeping print quality at a satisfactory level. The apparatus for discriminating sheet material will be described below in this respect.
As shown in FIG. 11, a bar 106 is rotatably supported near a positioning roller 103 (U.S. Pat. No. 5,962,861). A force F acts on an end 105 of the bar 106 in a direction shown by the arrow. Now, the bar 106 slightly rotates in a clockwise direction (see symbol E) as a printing paper P is fed, but a displacement thereof varies depending on the material of the printing paper. Thus, the kind of the printing paper P can be discriminates by detecting the displacement with a sensor 108.
In the conventional apparatus described above, the printing paper P should be deflected under only the influence of the lifting force F from the bar 106. However, the printing paper P may be deflected under the influence of wind pressure if the speed at which the printing paper P is fed is high, and the printing paper P may be deflected simply by its own weight if it is thin. Thus, in such a case, it is difficult to discriminate the kind of a paper correctly. In addition, the printing paper P is susceptible to mechanical vibrations.
Thus, the present invention is to provide a new apparatus capable of correctly discriminating the kind of a sheet material. So far as discrimination of a sheet material is concerned, the apparatus and method according to the present invention may be applied without being specifically limited, and also they may be applied even if the speed at which the sheet material is fed is high, and the sheet material is thin.